Modern Physics Flashcards
What is special relativity?
All the laws of nature are the same in all uniformly moving reference frames.
The speed of light is a constant, independent of the motion of the light source or the observer.
Motion is relative, and time is relative.
What occurs in one reference frame may occur in a different order in another reference frame. Simultaneous events may not be simultaneous.
u’=(v+u)/(1+((vu)/(c^2))
What does u’, v, and u stand for?
u’, speed of object relative to stationary observer.
u, speed of object relative to moving “ship”
v, speed of the “ship” relative to stationary reference frame.
Qualities of a particle.
Mass and volume. Kinetic collisions. Countable. Only exist in one place (localized)
Qualities of a wave.
Wavelength and frequency. Wave interference. Continuous. Over a large space (delocalized)
What is the photoelectric effect?
Ephoton=hf-W
Where Ephoton is the incident light energy, h is Planck’s constant, f is the frequency, and W is the work function (minimum energy to displace an electron).
A photon’s energy is proportional to its frequency. It takes a minimum frequency for a photon to have enough energy to displace an electron.
What did Max Planck theorize?
He theorized that metals begin to glow because their vibrating molecules can only vibrate at certain quantities of energy.
Forces could only be in little steps at a time. Energy released is not continuous, but is discretely released in packets of energy called quanta which is directly proportional to its frequency.
Planck’s Constant, h=6.63*10^-34Js
What is a black body?
A theoretical construct that absorbs all radiation reaching it and emits radiation. It does not reflect.
How is light similar to both particles and waves?
Light shows interference patters (wave). Photoelectric effect (particle).
Does light possess momentum?
Light possesses no mass, but has momentum.
What are the 5 possible interactions between light and matter?
- Reflection. Perfectly elastic.
- Photoelectric effect. Photon may free an electron and be absorbed in the process.
- Compton Effect. A photon may emerge with less energy and momentum after freeing an electron. Photon has lower frequency.
- The photon may be absorbed by an individual atom and elevate an electron to a higher energy level within the atom. The electron remaining is in an excited state. When the electron returns, the photon is released.
- A photon undergoes pair creation where it is converted into two particles with mass (this conserves energy and momentum because the photon’s energy is converted into kinetic energy of the new particles and their rest mass energy). It creates a positron and en electron.
These interactions all say that light must be a particle.
What did Young’s double slit experiment do?
Demonstrated conclusively that light behaves like a wave.
Also provided a way to absorb wavelength.
Wave Particle Duality.
All quantum objects, including electromagnetic radiation and electrons can exhibit interference.
How do quantum objects transfer?
In discrete amounts called quanta. (can be thought of as parcels of energy).
What did Louis de Broglie first propose?
All classical particles have wavelike properties.
Hypothesized that a photon has momentum p=h/wavelength.
From that, a particle with momentum may have a wavelength.
wavelength=h/p=h/mv
These are known as matter waves, not electromagnetic waves.
What makes electron microscopes possible?
All classical particles have wavelike properties.
What are the two “golden rules” of quantum mechanics?
- If a particle can be “here” or “there”, quantum mechanics allows it to be “here” and “there”.
- Rule 1 works as long as you don’t observe.
What is Heisenberg’s Uncertainty Principle?
There is a limit to how accurately simultaneous measurements of the position and momentum of a quantum object can be.
The very act of trying to measure the position of an electron affects its momentum and likewise for trying to measure the momentum.
What is the wave function?
A complete description of a wave/particle. Any information that cannot be derived from the wave function does not exist.
If two properties are related by an uncertainty principle…
no measurement can simultaneously determine both properties to a precision greater than the uncertainty relation allows.
How do you know how many electrons an element has?
It has equal numbers of protons and electrons. (Assuming no ionization).
What is u?
The atomic mass unit based on carbon-12, 6p+ and 6n
What is standard atomic notation?
E is the element, z in top left is atomic mass. a in bottom left is atomic number (number of protons).
How do you find the number of neutrons?
mass#-atomic#=neutron#
What are isotopes?
Atoms of the same element that have the same atomic number but different atomic masses due to a change in its number of neutrons.
What is radioactivity?
The spontaneous disintegration of a nucleus.
What elements are radioactive?
All above atomic# 83 and some isotopes of lighter elements.
What is an alpha particle?
Two protons and two neutrons. Also known as He+2
Positively charged. Slightly deflected in magnetic or electric field. Emitted at high speeds. Low penetration power (2cm in air). Can be stopped by a thin layer of paper or aluminum.
Results in the original nucleus changing; atomic# falls by 2, mass# falls by 4.
What is beta radiation.
An electron from inside the nucleus (or positron in some cases).
Greatly deflected in an electric or magnetic field. Travel at various speeds, some approach speed of light. Medium penetration power, up to 10m in air. Can penetrate several centimeters of aluminum. Results in original nucleus atomic# increasing or decreasing by 1.
In beta negative decay, a neutron can decay into a proton, emitting en electron and an antineutrino (incredibly small). Or, in beta positive decay a proton can decay into a neutron, emitting a positron and a neutrino.
What is gamma radiation?
A type of electromagnetic wave. (Photon)
High energy. Highest penetration power, 2km in air.
Can penetrate a minimum of 30cm of lead.
Composition of original nucleus does not change when these are emitted.
Energy given off in very short wavelengths (high frequency).
No mass.
Travel at speed of light.
No charge.
Often occurs alongside alpha or beta decay.
Often omitted in equations.
Gamma decay is a nucleus going from an excited state to a ground state.
What are neutrinos?
Similar to electrons, but carry no charge.
What radiation is the most penetrating?
Gamma. Followed by beta, and then alpha.
What are x-rays?
Electromagnetic radiation created when there is a change in the arrangement of the electrons in electron shells (QM).
What is neutron radiation?
Heavy particle with no charge emitted from nucleus by fission or bombardment by external particles.
Very few radioisotopes are direct neutron emitters (often they emit gamma rays as well).
Mass about equal to protons.
Highly penetrating due to lack of charge (less than gamma, more than beta)
